The invention relates to thermosetting aromatic prepolymers and to the thermally resistant thermoset polymers derived therefrom.
Thermosetting prepolymers are well known to be useful in many widely varied applications. For example, one of the most conventional thermosetting prepolymers, the unsaturated polyester resins are often used in the molding of glass fiber reinforced or other fiber reinforced products such as automobile bodies, aircraft parts, chairs, heater housings, trays, etc. Some of the advantages of thermoset polymer products over metals include lightweight, high strength to weight ratio, resistance to corrosion and part design flexibility. While such unsaturated polyester resins are typically suitable in the aforementioned applications, they generally do not possess the resistance to high temperatures needed to enable them to be suitably employed as parts for internal combustion engines, magnet wire coatings and other articles which are normally exposed to temperatures above 200.degree. C. In fact, when such polyester resins are exposed to such high temperatures for substantial periods of time, they undergo severe weight losses and loss of physical properties which are believed to be caused by the thermal oxidation of the thermoset polyester molecules. Moreover, such unsaturated polyester resins are multicomponent systems, consisting of catalysts, reactive diluents and the base resins. These multicomponent systems must be critically formulated before use and, once formulated, have only limited shelf-life.
Other thermosetting prepolymers that have been employed in applications similar to those employing the polyester resins include the epoxy and phenolic resins. All of such resins suffer from the same general lack of ability to withstand high temperatures for prolonged periods without significant weight loss and loss of other physical properties exhibited by the polyester resins. Furthermore, the reaction necessary to cure phenolic esins inevitably liberates volatile by-products, thereby creating undesirable voids in the cured resin. Thus, one-component resin systems which cure without the liberation of volatile by-products to cured products capable of withstanding prolonged exposure to high temperatures would be desirable.
Recently, e.g., U.S. Pat. Nos. 3,935,197; 3,845,018 and 3,882,073, attempts have been made to prepare such one-component resin systems. While such attempts have been successful to some degree, further increase in temperature resistance is required for acceptable utility as engine parts and the like. Moreover, such recently developed resins are generally difficult to prepare, involve the use of expensive starting materials and often require the use of very expensive solvents in their conversion to the desired fabricated products.
Therefore, it would be highly desirable to provide new thermosetting compositions which are easily prepared from relatively inexpensive starting materials and are readily dissolved in conventional organic solvents and which cure to form thermoset products exhibiting high thermal resistance.